1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a rim cavity sealing apparatus and process for the gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as an industrial gas turbine (IGT) engine, includes a turbine section with multiple rows of stator vanes and rotor blades in which the stages of rotor blades rotate together around the stationary guide vane rows. The stator vanes extend into a rim cavity formed between two stages of the rotor blades as seen in FIG. 1. Seals are formed between the inner shrouds of the rotor blades and the stator vanes, and between the inner vane U-ring and the two rotor disk rim extensions. The hot gas flow pressure is higher on the forward side of the stator vanes than on the aft side, and thus a pressure differential exists within the rim cavity.
In the prior art, the U-ring attached to the bottom of the vane assembly is used in the IGT engine design for the control of leakage flow across the row of vanes. A single knife edge seal is used on the blade cover plate to produce a seal against the hot gas ingestion into the rim cavity. Hot gas ingestion into the rim cavity is prevented as much as possible because the rotor disks are made of relatively low temperature material than the airfoils. The high stresses operating on the rotor disks along with exposure to high temperatures will thermally weaken the rotor disk and shorten the life thereof. Purge cooling air discharge from the U-ring cavity has been used in the cooling of the U-ring seal as well as to purge the rim cavity of the hot gas flow ingestion. However, very little progress has been made in the control of rim cavity leakage flow distribution for the reduction of the total purge air demand, especially for a large IGT engine design application. Due to the large pressure differential between the front rim cavity and the of rim cavity, the front rim cavity requires a higher purge air pressure than the aft rim cavity to prevent the hot gas ingestion into the forward rim cavity. Cooling air for both the forward and aft sections of the rim cavity is provided from the same pressure source which is typically through the U-ring. An open gap in-between the U-ring and the rotor disk will result in a purge air mal-distribution. A majority of the purge air will pass through the sealing gap and exit from the aft section of the rim cavity. In some cases, hot gas ingestion into the front or forward section of the rim cavity will result in the purge air mal-distribution effect.